Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.32   12.294%   $268.742   $268.74   $268.75   $268.70  
  Purchase #2 $61.66   13.299%   $69.8602   $69.86   $69.85   $69.90  
  Purchase #3 $147.51   11.253%   $164.1093   $164.11   $164.10   $164.10  
  Purchase #4 $140.41   11.724%   $156.8717   $156.87   $156.85   $156.90  
  Purchase #5 $181.78   12.607%   $204.697   $204.70   $204.70   $204.70  
  Purchase #6 $49.45   5.560%   $52.1994   $52.20   $52.20   $52.20  
  Purchase #7 $117.82   7.598%   $126.772   $126.77   $126.75   $126.80  
  7 purchase totals = $937.95       $1,043.2516   $1,043.25   $1,043.20   $1,043.30